Crescent pump gear systems consists of an inner gear and an outer gear located at an offset. The gear set operates in a sealed housing with the inner gear driving the outer gear in mesh at the top dead band. The bottom dead band is sealed using a crescent shaped section of housing between the major diameter of the inner gear and the minor diameter of the outer gear.
Crescent pump gear systems are typically used in pumps with high pressure applications since the sealing capability of the gears against the crescent is enhanced due to the number of teeth on both the inner and outer gears that seal across the crescent of the pump at any particular point in time.
Conventional crescent pumps usually have heretofore utilized involute gear forms. However due to the mathematical generated of involute curves the gear teeth on a crescent system utilizing involute gear forms will be small and require a large offset in order to function properly. This greatly reduces the displacement of the pump for a given pump size.
In the construction of gear pumps having a high output, significant value is placed on utilizing fewer number of teeth since fewer number of teeth will result in low tooth mesh or engagement frequency and consequently a low frequency noise is observed during operation.
Furthermore a small number of teeth is further desirable since it will result in larger tooth gaps and hence bring about a larger discharge or delivery volume and therefore increase the pumping characteristics of a given pump.
Various tooth profiles have heretofore been proposed.
For example U.S. Pat. No. 1,516,591 teaches that the addendum sections of an inner gear are formed on epi cycloidal curves while the dedendum sections are formed on hypo cycloidal curves. However this patent teaches that the generation of the epi cycloidal and hypo cycloidal curves of the gear teeth are the same in diameter.
Moreover U.S. Pat. No. 3,907,470 illustrates that the outermost flanks of two adjacent teeth on an annual gear wheel are defined by a circular arc or an arc of a curve equidistant from a hypo cycloid.
Moreover U.S. Pat. No. 4,504,202 illustrates a centred outer rotor for a rotary pump utilizing the trocoidal curve and manufacturing method for the rotor, whereby the rotor is formed to make a combinational gap between an inner rotor and the outer rotor as small and constant as possible in order that both the inner and outer rotors are rotatable.
Another device is disclosed in U.S. Pat. No. 4,518,332 which teaches an oil pump using internal gearing wherein the different in the number of teeth between the internal and external gears is one and wherein the inner rotor is directly connected to the crank shaft of the internal combustion engine or to the transmission shaft.
Finally U.S. Pat. No. 4,657,492 teaches a rotor for a rotary pump.
These and other gear sets and rotary gear pumps present relatively complicated structures which have relative utility.
It is an object of this invention to provide an improved crescent gear set and in particular to provide an improved crescent gear pump displacing more oil from an equivalent size gear set.
It is an aspect of this invention to provide a crescent gear set comprising; externally rounded toothed annular gear journaled for rotation about a first axis; and externally toothed annular gear rotatably engageable within said externally toothed annular gear about a second axis; a crescent contacting a portion of said internally and externally annular gears; said externally toothed gear having dual cycloidal tooth profiles generating about a first generating circle and said internally toothed gear having dual cycloidal tooth profiles generated about a second generating circle.
It is a further aspect of this invention to provide a crescent pump gear including; a housing having a chamber communicating with an intake port and a discharge port; a shaft journaled for rotation within said chamber; and externally toothed inner gear mounted centrally on said shaft about a first axis; an internally toothed annular gear eccentrically mounted for rotational engagement within said inner gear about a second axis; a crescent contacting a portion of said inner and outer gears; said inner gear having dual cycloidal tooth profiles generated about a first generating circle, and said outer gear having dual cycloidal tooth profiles generated about a second generating circle.
It is a further aspect of this invention to provide; a method of producing tooth profiles of externally toothed inner gears eccentrically offset and engageable with internally toothed annular outer gears, said inner and outer gears contacting a crescent having an inner crescent radius and an outer crescent radius, said method including the steps of: generating the pitch circle of said outer gear; producing an epi cycloid of a first cycloid set by rolling said epi cycloid in a clockwise direction about the pitch circle of said outer gear starting at the vertical axis for a full 180.degree. of roll; producing a hypo cycloid of a first cycloid set by rolling in a counterclockwise direction around the pitch circle of said outer gear starting at the vertical axis until the generated curve intersects at outer crescent radius; producing an epi cycloid of a second cycloid set by rolling in a counterclockwise direction about said pitch circle of said inner gear starting at an angle from the vertical axis equal to 360.degree. divided by the number of teeth of said outer gear minus two times the angle resulting from the length of roll of said first epi cycloid roll for a complete 180.degree.; producing a hypo cycloid of a second cycloid set by rolling in a clockwise direction about said pitch circle of said outer gear starting at an angle from the vertical axis equal to 360.degree. divided by the number of teeth on said outer gear minus two times the angle resulting from the roll of said first epi cycloid roll until the generated curve intersects said outer crescent radius; connecting the resulting gear profiles with an arc slightly offset from said outer crescent radius in order to provide running clearance; copying the resulting gear form about the centre of said pitch circle of said outer gear at increments equal to 360.degree. divided by the number of teeth of said outer gear; generating the pitch circle of said inner gear; producing an epi cycloid of a first cycloid set by rolling said epi cycloid in a clockwise direction about said pitch circle of said inner gear by starting at the vertical axis of said pitch circle of said inner gear until the generated curve intersects said inner crescent radius; producing a hypo cycloid of a first cycloid set by rolling in a counterclockwise direction about said pitch circle of said inner gear by starting at the vertical axis until the generated curve is slightly smaller in length than said hypo cycloid curve generated on said outer gear; producing an epi cycloid of a second cycloid set by rolling in a clockwise direction about said pitch circle of said inner gear starting at an angle from the vertical axis equal to 360.degree. divided by the number of teeth on said inner gear minus two times the angle resulting from a full 180.degree. theoretical roll of said first epi cycloid until the generated curve intersects at inner crescent radius; providing a hypo cycloid of a second cycloid set by rolling in a clockwise direction around the pitch circle of said inner gear starting at an angle from the vertical axis equal to 360.degree. divided by the number of teeth on the inner gear minus two times the angle resulting from the full 180.degree. theoretical roll of said first epi cycloid until the generated curve is slightly smaller in length than the hypo cycloid curve generated on the outer gear and is equal in length to the hypo cycloid curve generated by said first cycloid set; connecting the resulting gear profiles with an arc offset slightly from the connecting arc on the outer gear set to provide a running clearance; copying the resulting gear form about the centre of said pitch circle of said inner gear at increments equal to 360.degree. divided by the number of teeth of said inner gear; connecting the gaps left between said epi cycloids with an arc slightly smaller than the inner crescent arc in order to provide running clearance.